The invention concerns a procedure for controlling the density distribution of a bulk material in the manufacturing of particle board panels.
In the production of particle board panels, it is necessary that the stability properties of the finished panel be constant over the entire cross section of each panel. Particle board panels with non-uniform material characteristics result in rejects and adversely affect the usefulness of the product.
Since the thickness of the finished panel over the cross section of a particle board panel (Wood as Raw Material and Fabrication Material 40 (1982), p. 385) serves as basis for the individual stability values, it is necessary to achieve a predetermined density distribution prior to distribution of the chips onto the forming belt. This is critical since no change in the density distribution can take place in the subsequent pressing.
Thus, the purpose of the present invention is to compensate for errors in the density distribution over the pouring width which may occur even during the flow of the bulk material to the forming station.
This problem is solved in that prior to reaching the forming station, the stream of bulk material is subjected to mixing between a pair of rotating rollers. The procedural step of mixing prior to forming makes it possible to obtain a constant density of the quantity of bulk material over the entire width of the bulk material stream.
The apparatus of the present invention functions to control the density distribution of bulk material in the manufacture of pressed wood panels. An arrangement is provided for storing and delivering a stream of bulk material to a downstream location where the material is deposited upon a forming belt. A pair of spaced apart parallel rollers is provided intermediate the bulk material storage and the forming station. The stream of bulk material flows through the spacing between the rollers which spacing may be adjusted depending upon the desired thickness of the bulk material stream. The rollers rotate in opposite directions such that the inner surfaces thereof move in the same direction as the bulk material stream. Also, the rollers oscillate in a direction transverse to the flow of bulk material and the combined action of the rotation and oscillation renders uniform the density along the width of the bulk material stream. This is accomplished by shifting the excess portions of bulk material in the stream to those areas where more material is needed. Preferably each of the rollers has a smooth surface.
Also, the rollers may be mounted for movement along the stream toward and away from the bulk material storage while the bulk material stream is passing between the rollers. This action assists in rendering uniform the density distribution of the stream. A second roller pair identical to the first may also be utilized such that the stream of bulk material passes between the slotted opening formed by each roller pair.
The procedure according to the invention and the apparatus for executing this procedure can be applied in all production lines for manufacturing pressed wood panels such as particle board and fiber board. Thus, it is independent of whether the production is based on spreading or by means of a blower or a combination of these two distribution possibilities. The present invention is also similarly suitable for depositing chips for pressed wood directly onto a forming belt or on trays transported by a forming belt.